PROTEIN DIGESTIBILITY AND BIOACCESSIBILITY OF A1 AND A2 MILKS THICKENED FOR SAFE CONSISTENCY IN DYSPHAGIA

For individuals with dysphagia, adequate protein intake is essential both to preserve muscle mass and to prevent clinical complications arising from malnutrition. In this context, milk stands out as a nutritionally rich and easily adaptable food. Among the available types, the most common are A1 and A2, which differ due to a genetic variation in casein. In A1 milk, protein digestion may release the peptide β-casomorphin-7, associated with effects on gastrointestinal motility and with pro-inflammatory and immunomodulatory outcomes. The aim of this study was to evaluate protein content and protein bioaccessibility, using the in vitro digestion protocol INFOGEST 2.0, in A1 and A2 milks thickened according to the recommendations of the International Dysphagia Diet Standardisation Initiative (IDDSI). Skimmed A1 and A2 milks were purchased locally and thickened to level 3 of the protocol. Thickening was confirmed by the Flow Test, in which 8–10 mL remained in the syringe after 10 seconds of flow. A 3.6% concentration of a thickener based on maltodextrin, xanthan gum, and potassium chloride (as gelling agent) was used. Protein content was determined by the Kjeldahl method, and protein bioaccessibility was measured by in vitro digestion adapted from INFOGEST 2.0. Viscosities were measured using a SolidSteet viscometer. Statistical analysis was performed with the t-test using RStudio software. Both milks presented a protein content of 3.1%. Before thickening, A1 milk showed a viscosity of 584.1 mPa.s and A2 milk 269.2 mPa.s, both classified as IDDSI level 0. After thickening, values increased to 11420.50±345.78 mPa.s and 10654.80±1562.99 mPa.s, respectively, reaching level 3. A1 milk presented 1.96±0.07% of protein in the bioaccessible fraction and 3.58±1.46% in the non-bioaccessible fraction, while A2 showed 2.18±0.36% and 5.47±2.04%, with no significant differences between them (p>0.05). The higher content of non-bioaccessible protein may be related to the presence of the thickener, which hinders enzymatic access to protein molecules. Protein bioaccessibility corresponded to 63.23±2.28% for A1 milk and 70.48±11.63% for A2 milk, with no statistical differences (p>0.05). Nevertheless, even when thickened, A2 milk showed higher protein content and bioaccessibility than A1, suggesting that the β-casomorphin-7 peptide may interfere. These findings indicate that A2 milk may be a nutritionally more advantageous option for individuals requiring higher protein intake, and that both thickener choice and consistency assessment are crucial to ensure product safety and acceptance.